This invention relates generally to x-ray tube anodes and, more particularly, to applied coatings for enhancing the thermal emittance of x-ray tube anode targets.
Because of the very substantial amount of thermal energy created in the generation of x-rays, efforts are made to dissipate the heat from the x-ray tube target as fast as possible. A common approach has been to apply a coating of a selected material on the rear surface of the target to thereby enhance the emissivity of that surface to quickly dissipate the heat from the body of the target. This is shown in U.S. Pat. No. 4,132,916, wherein the coating applied is comprised of up to 20 percent by weight of a high thermal-emittance material TiO.sub.2 with the remainder of the composition being made up of an oxide for raising the melting point to an acceptable level and a small amount of a stabilizing material for stability the oxide over the operating temperature range. The primary reason for maintaining the percentage of TiO.sub.2 to a level at or below 20 percent by weight was that higher percentages of that material resulted in a liquid runoff from the surface of a molybdenum target when the coating was heated during the fusing process.
The above-mentioned coating has been successfully used with molybdenum targets. However, it has been found that when such a coating is applied to a target composed of a molybdenum alloy, such as the commercially available TZM or MT104, there are problems with both adhesion and surface fusing. The coating will not adhere to the alloy material as well as it does to the molybdenum material. Similarly, the inadequate surface fusing results in a very rough and particulate dominant surface. Such a surface is inadequate for purposes of high-voltage stability because of particulate spallation that would occur.
It is therefore an object of the present invention to provide an improved high thermal-emittance coating for x-ray tube targets.
Another object of the present invention is the provision for a thermal-emittance coating which adheres well to an x-ray target composed of a molybdenum alloy material.
Yet another object of the present invention is the provision in a molybdenum alloy target for a thermal-emittance coating having a surface that is fused to a smooth and glossy condition.
Still another object of the present invention is the provision for a molybdenum alloy x-ray target with an emittance coating which is economical to manufacture and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.